There are differences between the sexes. Female sperm whales tend to make more shallow dives than males, descending to about 1,000 feet below the ocean's surface, while males dive as low as 3,000 feet. Females cannot dive with their nursing calves, who are too young to hold their breath long enough to stay submerged with their mothers. At about one year of age, a young sperm whale begins feeding on its own. Its mother is never very far away, though, and responds defensively if a calf is threatened by a shark or killer whale. Male whales, called bulls, leave the pod when they are five years old, either to live alone or join bachelor pods of other young males. For the next 50 to 80 years, male adults live apart from the complicated social organization of females and children. Younger males live in small groups, while older bulls lead solitary lives. Males mingle with females only when it is time to mate.
SPERM WHALES: THE REAL MOBY DICK explains that beneath the water's surface, sperm whales reinforce social bonds by rubbing against each other. This rubbing presents the research team with a special opportunity: by collecting sloughed-off samples of whale skin, they can gather information to support their hypotheses, such as the idea that many members of a pod are related. Once collected, the samples are sent to a lab for genetic analysis.
Sperm whales' relatively peaceful lifestyle is fairly new, for they were heavily hunted by humans until 1987. In previous centuries, whale oil was used to light lamps and lubricate machines, and a single whale head can yield more than 600 gallons of pure oil. Ambergris, a substance found in the stomach of sperm whales, has long been used as an additive to perfumes to extend the life of its scent. A worldwide moratorium on hunting whales exists, passed in 1986 by the International Whaling Commission. However, Jonathan Gordon warns that whaling remains a large potential threat. "The moratorium has held," he explains, "but it looks as if it's about to crumble." In addition, as of 1998, Norway and Japan are in violation of the moratorium and continue to kill whales. Sperm whales are especially vulnerable, maintains Dr. Gordon, because they reproduce at a rate of less than one percent a year. What can ordinary people do to support whales? "It always pays to be vigilant," Dr. Gordon says. "Just be aware of the threats."Sperm Whales: The Real Moby Dick Home NATURE Home | Previous Features Menu Introduction | Meet Jonathan Gordon | Social Structure | Resources | Swimming With Whales PBS Online | Thirteen Online